A family friend recently died during a business trip. In his hotel room. Alone. Could have been me.

And according to United I've already traveled 18,641 miles in 2010.

I don't like the hassle of traveling. The excitement of visiting new lands has long past.

So why do I travel? The one-word answer: People. I like to meet my fellow colleagues, talk with them, make myself, my group, my field known and help shape future research. When you travel people make time for you and you make time for them in a way email and conference calls can't do.

Nevertheless I will make an effort to travel less, certainly while I have those last few precious years before my kids go off into the world. If you invite me some place and I turn you down, don't take it personally. I'm just trying to bring back some sanity into my life.

Monday, March 29, 2010

A while back I posted a list of books that I needed
reviewed for my column in SIGACT NEWS. This was legitimate--- I
really did want reviewers--- but it was also an experiment in
the power of this blog. Would I get more reviewers? How would the
quality of the reviews be?

The results are in: Roughly 40 people asked for books, and
35 are done. Of the 5 left 3 asked for extensions that were
legit. Only 2 were really derelict (of those 2, one returned
the book).
All the reviews I received were of high quality.
(If you only asked for an extension in the last month, then
you are the derelict one. No more book reviews for you!)

The experiment also indicates that far more people read this blog
then read my column, though I already knew that.
To extend the reach of my column I will begin posting it on
this blog when it comes out, with one change:

Here
is Volume 41, No. 1, 2010, SIGACT NEWS book review column.
Sort of. I intentionally OMITTED the
part where I ask people for books to review. That is because
the list that was with that column is already out of date.

I once again INVITE you to email me that you want to review a book.
Here is a list of available books.

Procedure: If you want to review a book then email me your postal
address to send the book to. The review should be ready about
3 months after you receive the book; however, that can be flexible
so long as there is some definite due date, past which I can
email you `HEY, WHERE IS THE REVIEW!'
If you are in America then I will postal mail the book to you
and it should get there fairly fast.
If you are not in America then (because of postal rates) I will have the
publisher send the book to you. It may be a while before you get it.

The sooner you ask for a book the more likely you are to get it.
I will try to update the list; however, you may end up asking for a book
that I already assigned if you see it before I update it.

Friday, March 26, 2010

Recall that Perelman was given the Fields Medal in 2006 for
proving the Poincare Conjecture.
He declined the award.

Recent news:
Quoting the Wikipedia article on Perelman:
Perelman was officially awarded the Millennium prize on March 18, 2010.
Note that they are giving it JUST to him. There was some discussion
earlier if there would be split credit of some kind.

Perelman's reasons for turning down the Millennium prize are likely similar
to why he turned down the Fields Medal.
To quote him on the Fields Medal:
I'm not interested in money or fame. I don't want to be on display like an
animal in a zoo. I'm not a hero of mathematics. I'm not even that
successful; that is why I don't want everyone looking at me.

Some random views I've heard about this: NONE are mine.

Turing down the Fields Medal ($15,000) is eccentric.
Turing down the Millennium prize ($1,000,000) is insane.

I have some sympathy. I have a grant and now I have to work
on the stuff it says to work on rather than the stuff I
later got interested in. Money and prizes should not guide research.
Wait, did you say its $1,000,000? My mistake, this guy is
not playing with a complete axioms set.

By turning it down the Fields Medal, and now the Millennium prize,
he gets more people to look at him like he's
an animal in a zoo. I doubt he planned that.

After turning down the Fields medal, if he had taken the
Millennium then it would look like he had compromised his ideals
(making him an ideal compromiser). But see the next item.

His reasons for turning either prize down do not seem idealistic.

It was rumored that Andrew Wiles locked himself in his
attic or basement for 7 years to work on FLT. This story is either
false or an exaggeration.
It made the rounds because it enforces the stereotype of a mathematician.
By contrast, Perelman's story IS true but is SO bizarre
that I do not think it enforces any stereotype.

Is Perelman still doing math? If he solves Riemann then he'll
save the Clay Inst. another $1,000,000.

What happens to the money? Do the other prizes all get increased by
1,000,000/6 ? Do they find another problem instead?

Some in Russia are saying he should have given it to charity.
On the other hand, the Clay Inst IS a charity, so in a sense
he did give it to a charity. Instead of helping Russian Orphans
he is helping Mathematicians.

I gave a talk yesterday on Wednesday about how Laci indirectly and
directly affected my early research career. My Ph.D. thesis was on
interactive proofs which Laci co-invented in 1985
as Arthur-Merlin games. When I graduated in 1989, I was lucky to get a
2-year position at the University of Chicago, a great theory
department with Laci Babai as its star. That 2-year appointment lasted
nearly 20 years, much because of the research I did with Laci those
first few years.

Even when we didn't co-author, Laci was an invaluable research. My
advisor, Mike Sipser, told me his approach to research in complexity:
Find the underlying combinatorial problem and solve that problem. I
took that a step further: Once I couldn't solve the combinatorial
problem I walked down the hall to Laci's office where he could often
find a simple trick that gave me what I needed.

Wednesday, March 24, 2010

It's spring break at Northwestern and as I write this Tuesday morning,
I'm on a plane from San Francisco to Denver on my way to Columbus,
Ohio. My kids have their spring break next week during my first week
of classes for the spring quarter. So no family vacation for me and
instead I'm bouncing around the country.

CCC is an NSF-sponsored program of the CRA that finds opportunities
for computer reasearchers programs in the NSF and other governmental
agencies. CCC acts like a facilitator, an interface between CS
researchers and governmental funding agencies and policy makers.

Monday, March 22, 2010

(REMINDER AND UPDATE:
If you are a a grad student you can apply for travel support for STOC 2010.
See
here for details.
One update on that: since registration and hotel information for STOC 2010 is
not posted yet, you can estimate it on your application, or say
+ registration, + Hotel. NOTE- deadline is Friday March 26.
If you are a professor I ask you to email the theory grad students at your school,
who don't read this blog (if there are any), about the travel support available.)

To welcome Lance back from his Blog Sabbatical here is a post that
will inspire comments like
When is Lance coming back?
I even tossed in a few mistakes to feed the grammar-trolls.
(Is ``grammar trolls'' hyphenated?)

Some states are banning cell phones while driving or texting while driving.
Not sure what I think of that.
Should they ban putting on makeup while driving?
How about arguing with your spouse while driving?
Maybe they should have a general rule about
driving under the influence of distraction.
But that is probably too vague.
On the other hand,
I think we can all agree that they should outlaw tweeting while piloting:

Sunday, March 21, 2010

My father Paul Fortnow passed away thirty years ago today. Five years ago I wrote about some of the lessons I learned from him.

Suppose I could go contact him back into time. What would I tell him?

I could tell him about his beautiful granddaughters.

I could tell him that his Red Sox won another world series in 2007 but some things don't change, it's the Yankees who are reigning champs.

I could tell him about a device in my pocket called an "iPhone" that lets me contact anyone, access nearly all public information and it plays music and movies too. A big improvement over the Sony Walkman.

I could tell him about how easily we can search for the most trivial information. I learned that he wrote a review article when I was just a baby, that the house he grew up in was torn down and replaced with the Marshfield city hall, and that he died just about the same time that JR was shot.

I could tell him the answer to the biggest mystery of his generation: FBI Agent Mark Felt was Deep Throat.

But most of I would tell my father that taking one children's aspirin every day reduces the risk of heart attacks and maybe, just maybe, I'd be telling him these things in person.

Friday, March 19, 2010

With spring quarter arriving, I will take a break from book
writing on P v. NP and come back to blogging. I hit my goal of getting
past the point of no return (about three draft chapters out of ten)
but writing a book is a slow process.

I've been hearing a bit of buzz about a new algorithm from Arora,
Barak and Steurer for unique games that I first saw in Luca's
blog:
Given a unique game where 1-δ fraction of the edges can be
satisfied, you can in time 2npoly(δ)
find a coloring that satisfies a constant fraction of edges.

Does this kill the unique games conjecture, that the unique games
problem is NP-hard? Not yet. For every
ε>0, there are NP-complete sets sitting in
time 2nε. It's possible that there is some
reduction from SAT to unique-games will have the property that to get
a smaller δ requires an algorithm with a running time whose
polynomial depends on δ.

But does it give evidence that unique games may now be false (right
after Khot won the Waterman award)? Any improvement
in the Arora-Barak-Steurer algorithm would yield a subexponential-time
algorithm for NP if the unique games conjecture holds.

But in the end it could go the other way. If no one improves on the
ABS algorithm in the next year or so, it will seem like we've hit
a barrier right at the edge of where the UGC could still be true.
Which will make us think that UGC could be true again and after a
while, ought to be true.

As Nietzsche might have said, what doesn't kill the unique games
conjecture will only make it stronger.

Wednesday, March 17, 2010

Now that I'm joining Univ. of Maryland, and there are at several
famous bloggers there, I may consider starting a new blog as well.
I'm not so sure that this happens at the end, but before that I want
to know what the others are thinking regarding a successful blog in
CS and its criteria especially now that we have quite a few years of
blogging in CS (e.g. see a list containing several of them in the
leftside of this blog). I ask some questions below. Feel free to
answer them or give any other comments. You may want to give even an
example if you feel like it.

Do you like blogs which put controversial posts (like FOCS/STOC
vs others) or the ones which only mention news? If you think both
are necessary for a successful blog give your percentages.

Do you like blogs who give short or even long proofs? Do you
think people are reading them carefully enough to justify the
effort.

Do you like blogs who mainly talk about their authors esp. their
achievements? In short do you like blogs which essentially say "How
great I am?". Again you may give percentages here if you think it is
not bad.

Do you like blogs which mention opinions of the authors
explicitly or the ones that only mention questions without answers?

Do you like blogs of short posts or long posts? Give an estimate.

Should a blogger answer the comments or it is not necessary?

If you do not like a person or its work should you mention
his/her name or you should never ever mention any names as a
blogger.

Do you like blogs who repeat others' posts? If so give an
estimate of how often you should do this.

Tuesday, March 16, 2010

One of the commenters on the post on the recent Turing Award and the Waterman award
pointed out that the context I gave lead to a discussion
that was NOT about the work of Chuck Thacker or Subhash Khot.
The commenter said:
Can you post this again without the additional context so that the community could write
some comments on their work
OKAY, consider it done.
Now, commenters, its up to you.

The Turing Award for 2009 was given recently to
Chuck Thacker LINK. See
here.
He developed the first modern PC.

The Alan T. Waterman award was given to Subhash Khot.
See here.
He formulated the Unique Game Conjecture and has proven many
consequences of it.

Monday, March 15, 2010

There is now a central website for the FOCS conference as a whole
here!!

In addition to links to the most recent and upcoming conferences one
useful item that is included are locations and direct links to all the
past proceedings on the CSDL and IEEExplore since these are not always
easy to find from the IEEExplore search feature directly. (CSDL is
pretty good). Proceedings from all prior FOCS conferences are up on
the website and linked in. (The 50th FOCS is up on CSDL but not yet on
IEEExplore.)

FYI: CSDL is the Computer Society's digital library. IEEExplore is for
all of IEEE. Institutions subscribe to one or the other. The CSDL is
smaller (since it only does the Computer Society) and cheaper and
returns more money to the CS than IEEExplore does which is why the two
haven't merged.

Thursday, March 11, 2010

There are some theorems that are surprising.
I've already blogged on that (I can't seem to find the link).
However, there are some theorems that some people
simply do not believe.
I mean people who understand the proofs and still don't
believe them.
Let me give you a contrast- I DO believe that NSPACE(n) is closed
under complementation because, while surprising, the proof really
does tell you why its true. For the following surprising results
the proof does not help. Or at least does not help the people who
were surprised by it.

Barrington's theorem. I've read it, talked to Barrington about it,
and even taught it. I still don't believe that (say)
the set of strings that have the number of 1's equivalent to 0 mod 101
can be done by a width 5 branching program.

Banach Tarski Paradox
A CS grad students who knows some math says that it shows
that mathematics is broken. I would prefer to say it casts doubt
on the axiom of choice.

The rationals and naturals are the same size.
I know someone who knows the proof and is happy to say
they are the same cardinality but refuses to say
they are the same size. (I think they are wrong and this is
important- using the term size DOES matter.)

A well known theorist told me that he used to believe
both P ≠ BPP and there were problems in DTIME(2O(n)) that require
circuits of size 2&Omega(n);.
Oh well.

Lance Fortnow tells me he has a hard time believing the Recursion Theorem.
Perhaps because the proof is completely uninformative.
(Ted Slaman, a well known recursion theorists, agrees that the proof is
uninformative.
Bob Soare thinks the proof is quite intuitive- a failed diag argument.)

Local Lovasz Lemma
has gone from being something I didn't believe to something I
now understand and believe. The original proof just looked like symbols
being pushed around, but Moser's and later Moser-Tardos's constructive versions
makes sense to me.

We all know that Godel's theorem surprised people- but were there
people who did not believe it?
This theorem does not surprise Generation Xers who are not at all surprised
to find out certain problems cannot be solved. Their response: Whatever.

The existence of Geometries that are as valid as Euclidean but not Euclidean.
Again, this surprised people, but were there those who did not believe it?
In this age of moral relativism people have no problem with different geometries
that are all valid.

Wednesday, March 10, 2010

The Turing Award for 2009 was given recently to
Chuck Thacker LINK. See
here.
He developed the first modern PC.

The Alan T. Waterman award was given to Subhash Khot.
See here.
He formulated the Unique Game Conjecture and has proven many
consequences of it.

These two award recipients demonstrate the
vast variety there is within computer science.
I suspect that these two people, one very practical,
one very theoretical, have very different mindsets.
The most striking is that in theory we have PROOF as
our... proof that something is true (I can't even escape
using the word!). In practical things the proof is in the pudding.

There is much less variety within Mathematics.
All (well... most) mathematicians have proof as their criteria of truth.
They may not understand each others problems and interests but
they understand the type of problems each other works on.
Physics has two campus- theorists and experimentalists.
But I get the impression they talk to each other and understand
each other. While this is true in some parts of computer science
(crypto and bio-comp come to mind) it is also often not true.
(If I am wrong about Physicists let me know.)

Consider the following statements, both probably exaggerated.

In a math department any professor can teach any undergraduate class.

In a computer science department it is NOT the case that every professor
could PASS every undergraduate class.

Tuesday, March 09, 2010

The last blog entry had lots of good comments about
different HW policies. I enumerate them and say PROS
and CONS

Hard Deadline. PRO- uniform, no favoritism, can post HW Solutions or
go over HW in class as soon as it is handed in.
CON- there could be legitimate reasons for lateness
that are short of a doctors note.
CON- you want the student to DO the HW even if it will be late.
CON- you need to be TOUGH to say NO.

Moral Deadline (what I do, see last post).
Same as Hard Deadline, but its a bit easier to say NO.

Penalty for lateness.
PRO- the students will still do the HW.
CON- delay in posting solution.
CON- slackers are still slackers.
ODDITY- the penalty is supposed to discourage lateness.
But it may encourage it
(gee, 10% off if I hand it in one day late. OKAY, its a deal)

Look at late HW only if they affect the final grade.
PRO- less to look at likely,
CON- Don't really want to keep track of these things.
CON- student may not be discouraged from handing things in late.

Only count (say) 10 of the 12 HWs, and have HARD DEADLINES.
PRO- same as HARD DEADLINE.
CON- students will blow off 2 HW's, possibly the last two
which may be important for the final.
CAVEAT- raises the much bigger question of whether to treat
students like adults or like ...students.

Students get x number of late days (this one was new to me).
PRO- well defined rule, flexible but no favoritism.
CON- delay in posting solutions.
CON- keeping track of it.

If you miss a HW then the others will count more
(up to some limit).
PRO- uniform.
CON- students may still miss some HW they should do.

HW are OPTIONAL.
PRO- they sink or swim on their own.
CON- they sink or swim on their own.

Diff topic- how much to COUNT HW?
I often count it low (like 10-20 percent) so that I don't' have
to worry too much about cheating. Actually I think its GOOD
if students help each other but BAD if students copy each other,
but it can be hard to tell.

Which of these work best? Depends alot on the school and the course
and even the profs willingness to say NO.

Monday, March 08, 2010

HW is due on Tuesday. However, your dog died!
Hence you get an extension to Thursday.
That is, for all people in the class I assume you have
a quasi-legit reason to ask for an extension to Thursday.
Hence you can hand it in Thursday for full credit.
However, if you want an extension past that you will
not get it since I already gave you an extension
to Thursday. (There may be some severe exceptions which
will have to be documented.)

This will save alot of time in terms of students asking
permission to hand it in late since I will say
I already have you an extension and you are asking for
another one?

Some students will get into the habit of handing it in Thursday.
This is okay so long as they do not ask for an extension past that.

Clyde tells me that this is really a cheat- the HW really is due
Thursday. I may have a higher moral ground when telling them they
can't hand it in later than Thursday, but they will still feel
that they deserve an extension if their dog dies on Wednesday.
My response: they do not.

I do make sure that they have enough knowledge to do the HW
by Tuesday.

I am teaching one Junior-Senior class and one honors-class so
these are already pretty good students. They (I hope) know what
I mean when I say that they cannot ask for an extension past
Thursday. Also they will likely not need them.
I have not tried this in a Freshman class. I would like to
but they are usually co-taught and large so it would be
harder to manage.

Thursday, March 04, 2010

in honor of Rajeev Motwani (1962 - 2009)

Submit contributions by July 30, 2010.

Submissions in all areas of theoretical computer science
will be considered, with preference for topics related
to Rajeev's work. All papers undergo strict peer review
and must meet the standards of Theory of Computing.

Wednesday, March 03, 2010

Alice and Bob want to sent a message so that even if
Eve intercepts it, she cannot tell what it is.
We will allow Alice and Bob a short private meeting to exchange information
(or perhaps they will use RSA or Diffie-Helman for that).
But the key can't be that long and has to be reusable
(so one-time pad does not qualify).
I describe below a well known cipher
called the
Hill Cipher.
I think that there are circumstances where it could do well; however,
I am curious what you think.

Let n be a parameter we pick later.
Alice generates a random n x n matrix of
elements from {0,...,25} and checks that
the Det mod 26 is nonzero.
(CORRECTION ADDED LATER: the Det has to have an inverse
mod 26, so has to be rel prime to 26.)
Alice gives this to Bob.
Alice and Bob both compute its inverse.
Alice and Bob can exchange messages by encoding
every block of n by this matrix.
So the first n letters of the text get multiplied
by the matrix to get a diff n letters.
Then the next n letters after that, etc.

n has to be small enough so that Alice and Bob don't mind
exchanging n2 elements of {0,...,25}

n has to be large enough so that going through all possible
n x n matrices is not practical for Eve.

n has to be large enough so that tables of how often
particular n-sized blocks occur are useless.

Can combine with other techniques. Perhaps Alice and Bob
first encode using the
Vigenere Cipher
and then apply the Matrix.
They would then have to also share the Key for the Vigenere Cipher.

QUESTION: If ALL Eve gets is the text then is this a good cipher?
Clearly if Eve also somehow gets her hands on a message and what it was coded
to she will easily crack the code. But if not then does this work well?
This code is not used because Eve might get her hands on such,
but I wonder if these are circumstances where it would be reasonable.

Is there a value of n that is both big enough and small enough
(a Goldilocks n).

Monday, March 01, 2010

Based on titles alone (not so reliable) it looks like
there are no quantum papers. Someone tell me- is that
really true?
Even if there are some, I am sure there are not many.
Has the field run its course? Doubtful. In fact, it may be
the other way around--- the field has grown and their are
other places for that work to appear.

ADVICE: Try to download some of the papers that (1) interest
you AND (2) you have the prereq knowledge OR always wanted
to get that knowledge.
Either read them or use them to find refs to read.

Is there a centralized place to download them?
There should be!!!!!!
Other conferences manage this (SODA for one).